The present invention relates to a keyboard apparatus, and more particularly relates to an improvement in tone generation on a keyboard apparatus used for musical instruments such as electronic organs, electronic pianos and portable keyboard musical instruments in which a plurality of keys are swingably mounted to a fixed key support and a change in electric inductance is induced in response to every key operation in order to control musical tone control parameters.
Tone generation of an electronic musical instrument is conventionally controlled in response to key operation by means of a key switch attached to each key on a key support. Such a primitive way of tone generation control is too simple in characteristics to reflect player's emotion with complete fidelity. In an effort to meet with demand for richer reproduction of player's emotion during performance, the art of touch response was developed. In the case of this system, the keyboard apparatus has a function to adjust its tone generation in correspondence to finger pressure at key operation. More specifically, the tone volume, the tonal pitch and the tone colour of a tone to be generated are controlled in accordance with finger motion of the player at the beginning of the key operation and during the subsequent period of tone decay.
One example of such a touch response system is proposed in Japanese Utility Model Application Laid-Open Sho. 58-42890 in which an electrically conductive plate is attached to each key for causing a change in electric inductance and a coil is attached to a key support for detecting the change in inductance. At every key operation, the gap between the conductive plate and the coil varies to cause a change in inductance and the change is issued from the system in the form of a detection output.
In the case of this system the gap between the conductive plate and the coil varies at every key operation but without any change in the mating surface area between the two counterparts. With this system mechanism, there exists a parabolic relationship between the magnitude of the detection output and the extent of movement of the key (hereinafter referred to as "key stroke"). As a consequence, uniformity in detection outputs for a number of keys is greatly swayed by an inevitable structural error of the keys which is resulted from error in an interval between adjacent keys, in position of keys, in attachment of the conductive plate and/or the coil to each key and in other production factors. Presence of such inter-key variation of the detection outputs poses subtle, malign influence on tone generation by the system.
In the systems disclosed in Japanese Utility Model Application Laid open Sho. 60-125695 (U.S. Pat. No. 4,615,252) and Japanese Utility Model Publication Sho. 54-20990, a key operation signal and an after-control signal are generated separately. Separate generation of the two different signals, however, inevitably necessitates use of a complicated circuit construction. In addition, such an after-control signal cannot be obtained for an individual key. Provision of separate after-control signals for separate keys necessitates use of a further complicated circuit construction.